Over the last two decades, millet prices in Niger have enjoyed periods of spectacular growth followed by rapid reversals. During these periods of boom, millet prices seem to deviate from fundamental values. These deviations may be attributed to the presence of rational speculative bubbles. Considering millet as a "food asset" we develop a millet pricing model and test for the presence of periodically and partially collapsing bubbles for 15 millet markets of Niger. The test strategy consists in estimating price deviations from fundamental values and exploiting the theoretical properties of bubbles. The residual augmented least squares (RALS) Dickey-Fuller tests do not rule out the presence of bubbles in millet prices. Moreover, the estimation results from a M-TAR model that captures the asymmetries in the adjustment process of prices to fundamentals, do not reject the presence of rational bubbles for most of the sample markets. Lastly, an attempt is made to identify the origin and collapse date of bubbles using recursive and rolling ADF tests. Results show that small markets, located in deficit and remote areas are more prone to speculation than larger markets of the main producing and consuming regions.